Method of protecting lenses



June 16, 1953 A. H. PFUND 2,642,367

METHOD oF PROTECTING LENsgs Original Filed Jan. 9, 1950 I INV NTO .00605771 PFU/1 R Patented June 16, 1953 METHOD oF rRo'rEoTING LENsEs August Herman Pfund, Baltimore, Md., assignor to the United States of America as represented by the Secretary ofxWar Original application January v9, 194,7, Serial No.

`721,078. Divided and this 27, 1950, Serial No. 152,204

3 Claims. (Cl, 117-106) The invention described herein may be manufactured and used by or for the Government for governmental purposes Without payment to me of any royalty thereon.

This application is a division of my co-pending application Serial No. 721,078 led January 9, 1947, Which is now Patent 2,512,257 of June 20, 1950. Briefly stated the invention comprises a method of making rock salt and silver chloride lenses insensitive respectively to- Water and to ultra-violet light by coating said lenses While warm with a product produced by melting crepe rubber and thereafter eliminating solids from the product or coating a rock-salt lens rst with alkyd resin varnish and then applying to the lens a sheet oi polyethylene Ioxide resin or rubber hydrochloride. In the case of the silver chloride lenses, these are protected by coating them in vacuo With antimony trisulde or amorphous selenium thickly enough to give the lens'a deep orange or red color by transmitted light.A

An object is to provide a method for protecting rock salt plates or lenses against Water While still retaining their infra-red transparency.

Another object is to provide a method for light-proofing silver chloride lenses against u1- tra-violet rays While still retaining -their infrared transparency for rays up to l2 mu in Wave length.

application March gether before the cement solldiiies. It is also permissible to coat the SbzSs or Sez coated AgCl lens with the cement I3 before bringing the lenses together, provided the excess coating material is squeezed out when the lenses are broughtv together.

STOCK SOLUTION A Some pale natural crepe-rubber is melted down in a crucible. AT'he resultant dark, viscous mass remains fluid even at room temperature. To remove solid particles, some benzene is added. From. thissolution, the solid particles settle out. The liquid is then decanted. This liquid material is applied to the rock-salt lens I0 and the latter is then heatedto 60-70 C. to drive oi the benzene. After cooling to room temperature, the AgC'l lens or its equivalents, Which will now be disclosed, are mounted on the rock-salt lens Y as previously described.

sTocK SOLUTION B There is prepared a saturated solution of I paraffin (M. P. 60-68 C.) in benzene at a temperature of 30 C. Of this solution, 60 parts arev added to 40 parts of self-curing cement of the typewhich contains a vulcanization accelerator capable of vulcanizing the rubber at ordinary temperatures. If flakes of paraihn appear, more benzene is added to form a homogeneous solu- Another object is to provide a method for 30 tin.

.1 n jollrnloasvailgmllg elelofldfo t and Equivalents of the silver chloride lens Il is a lens of silver chloride. I2 is a coating of Equivalent A.-The rock salt lens I 0 is rst antmny tri-sulfide (Sb2S') 01" 0f amorphous protected on its edges by coating them with selenium (Sez). Such Coating iS applied to a dry, 3;-, varnish made by the interaction of glycerol and polished AeCl lens, which is free from grease, by phthalic anhydride, and which is an alkyd type vacuum distillation. The coating material iS resin varnish of the gradeused to seal evacuated volatilized in a high vacuum t0 which the AgCl spaces. Then a sheet of syntheticrresin of the lens is also subjected, so that the evaporated kind made by polymerizing ethylene with vinyl SbzSa or Sez Will (ZORG-GDS@ 1111011 the C001 16115- 40 acetate is applied. The synthetic resin sheet is The deposition is continued until the lens be- 'preferably 0 025 mm thick 'Chemically it is becomes a deep orange or red color by transmitted lieved to be a poiy-tethyiene-oxide. The sheet is light. A silver chloride lens so protected will not intended to project beyond the edge of the Girturn black 'after Several hOurS @XIJDSIUI'H` t0 a cular rock salt lens by 1 to 2 mm. so that when mercury are lamp of ordinary intensity. .f5 a close-fitting'brass ring having an internal The rock salt lens I0 also has a Coating I3. shoulder is slipped over the compound lens, the It is applied by the addition of a few drops of a sheet is held firmly npqace' l solution known as Stock Solution A, the prepara- Equivalent B.-A sheet of partially saturated tion and COIIIDGSOII 0f Which iS abut be de rubber hydrochlorides' of 0.02 mm. thickness is scribed. It iS adapted t0 act 3S a Cement as Well 5o substituted for the synthetic resin kiilm in the as a water-resisting compound, thereby insuring preding paragraph, 'The procedure is the the adhesion of the AgCl lens I I to the rock salt sauneI lens I 0. The cement or coating I3 is squeezed Equivalent Q Some 0f the Hquid knbwn as out to a very thin layer by using a glass tube as Stock Solution B is poured on the horizontal top y a roller. The two lenses are then brought to- 55 surface or" a polished rock-salt plate, mounted axially on the vertical shaft of an electric motor. The speed of rotation is the lowest (less than 10 per second) which will yield a flat layer of liquid at the center of the plate. This speed is maintained for about 20 seconds (to give the benzene an opportunity toIV evaporate somewhat), whereupon the speed is increased greatly to fling off the thick layer of liquid at the edge. The rocksalt plate and coating are laid on a cold metal plate which is heated gradually toa temperature of about 120 C., when the system is laid on a stone slab and is allowed to cool to room temperature slowly. Since a single coat does not offer adequate protection, a second, and possibly, a third coat must be applied, To ybe sure', if one waits -6 days, the self-vulcanizing rubberwill have become insoluble in benzene so that a sec- 0nd coat may be owed on the iirst without dissolving the latter. To avoid so great a delay, an extremely thin film of nitrocellulose is spread overthe top of the first coat. This is accomplishedby allowing a drop of a dilute solution of nitrocellulose in amyl acetate to spread out on a water-surface. When the volatiles have evaporated, the lm should show brilliant first-order interference colors. The iilm is lifted oir the Water by rnc-ans of a square metal plate measuring 3 X 3 inches, with a circular central hole 2 in diameter. While the rock-salt plate is still very het after the rst heating, but below the v' decomposition point of nitrocellulose, the dry nitrocellulose 'hlm is laid on the coating so that no air-bubbles are formed. When this syst-ern has cooled down to-roornY temperature, a second coat oi stock solution B may he applied. It is to be emphasized that-the total thicknessof coating ought to be no less than 0.03-Inn. After the last coat hasheen applied, a nallayer of nitrocellulose may be applied toi-improve the optical polish of the surface. lose frills upon prolonged exposure to saturated water-vapor, it is advisable to add a little parafn to the nitrocellulose solution from which the last lrn is formed.

Since straight ntrocellui' Films thus formed protect rock-salt against saturated water-vapor for more than 24 hours, and against water-drops for more than two hours. The overall transmission in the wavelength interval 8-12 mu is better than 70 per cent.

The equivalents are preferred in the same order that they are discussed.

The invention claimed is:

1. The method of protecting the surface of a lens which is made from a salt of silver normally decomposihle at the surface thereof by ultraviolet light, which comprises Vaporizing in a high vacuum a protective coating chemical selected from the group consisting of antimony trisuliide and amorphous elemental selenium, condensing the vapors thereof upon the surfaces of said lens and continuing the process until the lens appears deep orange to red by transmitted light, whereby said lens is lightproofed against ultraviolet rays.

2. The method set forth in claim 1 in which the salt from which the lens is made is silverl chloride.

3. The method of making a silver chloride lens insensitive to ultra-violet light which comprises vaporizingi antimony trisulde in a high vacuum, condensing the antimony trisulde vapors upon the surfaces of said lens and continuing the proc-A ess until the lens appears deep orange to red by transmitted light, whereby said lens is lightproo'fed against ultra-violet rays.

AUGUST HERMAN PFUND.

Referenties cited in the 'sie of this patent UNITED STATES PATENTS 

1. THE METHOD OF PROTECTING THE SURFACE OF A LENS WHICH IS MADE FROM A SALT OF SILVER NORMALLY DECOMPOSIBLE AT THE SURFACE THEREOF BY ULTRAVIOLET LIGHT, WHICH COMPRISES VAPORIZING IN A HIGH VACUUM A PROTECTIVE COATING CHEMICAL SELECTED FROM THE GROUP CONSISTING OF ANTIMONY TRISULFIDE AND AMORPHOUS ELEMENTAL SELENIUM, CONDENSING THE VAPORS THEREOF UPON THE SURFACES OF SAID LENS AND CONTINUING THE PROCESS UNTIL THE LENS APPEARS DEEP ORANGE TO RED BY TRANSMITTED LIGHT, WHEREBY SAID LENS IN LIGHT-PROOFED AGAINST ULTRAVIOLET RAYS. 